The present invention relates to power transmission drive systems for business machines and more particular to a drive belt having a plurality of equally spaced contour teeth that functionally engage corresponding equally spaced teeth of a pulley.
Noise associated with the transmission of power in high speed drives has always been an undesirable characteristic. Efforts to reduce the noise generated by high speed drives, in particular in business machines such as typewriters, have met with limited success.
Positive drive pulley and belt systems that operated at high speed usually generate objectionable noise to the surrounding environment. The origin of the noise can be attributed to a combination of factors; namely, the high rotational speed and the small motor pulley diameter that is necessary to obtain the desired speed ratios, and the initial contact of the belt teeth with the pulley teeth.
Although business machines in general are subject to noise generated by high speed positive drive systems, typewriters have been selected for purposes of this disclosure to emphasize the effect of noise in a quiet office area.
With the advent of portable electric typewriters, most of which are used in quiet environments, noise became increasingly more noticeable and disturbing. The efficiency of persons who require concentration or uninterrupted conversation with others has been known to be adversely affected by extraneous sounds. Cognizant of the desire for greater noise suppression in such equipment, typewriter manufacturers have implemented costly research programs to reduce the noise emission of typewriters and in particular, the drive system thereof.
Improvements to reduce the noise emission of typewriters have been attempted over the years, but none have been successful to a degree so as to meet with complete public acceptance. Efforts to reduce the sound vibrations initiated by the drive systems of business machines have also been made over a long period of time.
For example, U.S. Pat. No. 2,937,538 teaches a belt having teeth with convex working faces that cooperate with the plane faces of gear teeth to provide a quiet drive system. The quiet drive system results from the conjugate relationship of the faces of the gear teeth and the belt teeth where the convex working face of the belt teeth imparts a cushioning effect between the belt and the gear when engaged by the plane faces of the gear teeth.
Another example of a silent drive belt is disclosed in U.S. Pat. No. 2,815,671 which teaches a drive belt having wear resistant resilient rubber teeth united by a cushioning layer of softer rubber to an endless flexible load carrying band. The resilient rubber teeth in combination with the softer cushioning layer of rubber attached thereto contact the harder pulley teeth to produce a silent operating belt.
The above prior art has provided reduced noise transmission by high speed drives, but has not accomplished the degree of quietness required in a drive system of a business machine. Furthermore, the prior art has attempted to accomplish noise reduction in a manner that is substantially different from the present inventive concept.
The present invention relies on minimum and efficient driving contact between the belt and the pulley and depends entirely on the contour of the teeth of the belt and valleys therebetween, used in conjunction with a conventional positive drive pulley to transmit power from one location to another with slippage between the belt and the pulley. This structure results in minimum and efficient driving contact between the teeth of the belt and the teeth of the pulley to result in a quiet drive system.
The term "valleys" referred to in this disclosure, includes that portion of the belt from the base of one tooth to the base of an adjacent tooth including the opposing faces thereof.
U.S. Pat. No. 2,937,538 teaches full contact between all teeth of the belt and the pulley and further teaches belt teeth having convex working faces in conjugate functional relationship with plane working faces on the teeth of a mating pulley. To obtain a quieter drive system, the belt teeth include convex working faces to provide a rolling contact with the plane faces of the pulley teeth and further provide a cushioning effect between the belt and pulley. The full functional contact between the teeth of the belt and the teeth of the pulley is not desirable in that excessive noise is generated by the initial contact therebetween. The contact surface being related to the noise generated.
The present invention has as its primary purpose to provide a minimum functional contact between the belt teeth and pulley teeth. The minimum contact of the belt teeth and pulley teeth results in a power transmission drive system where noise normally generated by such devices is substantially reduced.
U.S. Pat. No. 2,815,671 teaches a positive drive belt having conventional teeth thereon in spaced relationship. The teeth are united by a cushioning layer of soft rubber to an endless flexible load carrying band. Therefore, when the belt teeth functionally engage a pulley, the engagement is cushioned by the fact that the cushioned layer structure of the belt yields under the driving load on the belt. This patent also teaches full contact between the teeth of the belt and the teeth of the pulley. Although the belt is provided with a cushioned structure to impart quietness to the drive system, the full contact between the teeth of the belt and the teeth of the pulley allows initial contact noise to occur, the prevention of which is one specific object of the present inventive concept. It has been found that a slopping noise is prevalent in conventional high speed positive drive belt and pulley systems where the teeth of the belt and the teeth of the pulley are in full contact.
The term "conventional high speed positive drive belt" referred to in this disclosure is an endless flexible power transmission belt having conventional spaced teeth projecting therefrom.